函数参数传双指针

class Test 
{
public:
  Test() {}
private:
  int a;
};
void fun(Test *tt)
{
  tt = new Test();
  std::cout << tt << std::endl;
  return;
}
void fun(Test **tt)
{
  *tt = new Test();
  std::cout << *tt << std::endl;
  return;
}
int main()
{
  Test *t = nullptr;
  //fun(t);
  fun(&t);
  if (t == nullptr) {
    std::cout << "t is nullptr" << std::endl;
  }
  else {
    std::cout << t << std::endl;
  }
  return 0;
}